1. Field of the Invention
The present invention relates to a parallax barrier filter realizing far higher brightness than a conventional barrier-type filter, and applicable to a flat display such as a liquid crystal display and a plasma display, for instance.
2. Description of the Related Art
Autostereoscopic three-dimensional displays that allow an image on a flat display to be viewed as a three-dimensional image without the need for a viewer to wear glasses have conventionally been available. Conventionally known autostereoscopic three-dimensional displays include those of a lenticular lens type that have a lenticular lens 110 placed in front of a flat display 112 as shown in FIG. 13 and those of a barrier type that have a parallax barrier filter 120, which is a black mask, placed in front of a flat display 122 as shown in FIG. 14. Among them, those of the barrier type have been conventionally mainstream autostereoscopic three-dimensional displays because of their low manufacturing cost and their ability to produce a high stereoscopic effect.    [Patent Document 1] Japanese Patent Application Laid-open No. 2004-239980
However, the barrier type has a drawback that images become dark because it is necessary to mask part of light coming from the flat display 122 by the parallax barrier filter 120 shown in FIG. 14. Further, in order to suppress reverse view and to increase the range of right observation, which means that images that the right and left eyes should view reach the opposite eyes, and to obtain a high stereoscopic effect, it is necessary to use three- or more multiple-parallax image instead of two-parallax stereo image.
However, as the number of parallaxes that is equal to or more than three and is not likely to cause moiré, a multi-parallax image such as a five- or eight-parallax image can be considered, for instance. Therefore, it is necessary to use a multivision filter using any of these numbers of parallaxes, but this results in an increased amount of light masked, and tends to further darken the image.
For example, in designing a conventional parallax barrier filter, when it is of an eight-parallax type, a ratio of transmissive areas (apertures) to opaque areas (mask areas) of the filter is 1:7. Therefore, brightness becomes one eighth compared with that without the parallax barrier filter, and thus only a dark image can be obtained.
Hereinafter, a conventional art will be described based on a conventionally used parallax barrier filter.
Firstly, in a flat display 132 shown in FIG. 15, a large number of picture elements are arranged vertically and laterally in matrix. Note that one pixel P forming one picture element is composed of three sub-pixels, that is, an R sub-pixel SP1 emitting red light, a G sub-pixel SP2 emitting green light, and a B sub-pixel SP3 emitting blue light (hereinafter, they will be sometimes collectively called an RGB sub-pixel). R, G, and B written on the upper side of the flat display 132 each indicate that red light, green light, or blue light is emitted from each one array of sub-pixels thereunder.
The conventional parallax barrier filter 130 shown in FIG. 15 is designed so that a width of each of apertures 134 serving as transmissive areas of the filter is equal to a width of one sub-pixel of a liquid crystal display or a plasma display being the flat display 132. For example, in the eight-parallax type, the aperture 134 is disposed only per eight sub-pixels in one array along the lateral direction.
Further, as shown in FIG. 15, in each of arrays vertically adjacent to the array having these plural apertures 134, the aperture 134 is similarly disposed only per eight sub-pixels along the lateral direction. However, the apertures 134 in the adjacent arrays are disposed to deviate from each other by one sub-pixel on the whole. Therefore, in the entire parallax barrier filter 130, the plural apertures 134 are arranged obliquely.
As a result, when the image is viewed through the parallax barrier filter 130 from a certain direction, every eighth sub-pixel SP1, SP2, SP3 is seen in the single array. This implies that brightness of the image from the flat display 132 is reduced to one eighth. Thus, the images each placed at every eighth sub-pixel among sets of the eight parallax images arranged in the lateral direction with one sub-pixel deviation form a three-dimensional image on the flat display 132.
Specifically, the plural apertures 134 of the parallax barrier filter 130 are arranged obliquely as shown in FIG. 15. Therefore, the single parallax image among these eight parallax images is disposed at every eighth sub-pixel in the lateral direction, and these single parallax images are arranged obliquely with one sub-pixel deviation. Note that the numbers 1 to 8 on the flat display 132 in FIG. 15 are numbers representing the order of the parallaxes.
Here, composite matrixes being matrixes for creating a three-dimensional image by combining the parallax images are shown in FIG. 16. FIG. 16 only shows M1 to M4 corresponding to four parallaxes among M1 to M8 forming eight parallaxes. In FIG. 16, 1 represents transmissive areas (apertures) and 0 represents opaque areas (mask areas). Further, as shown in the following mathematical expression 1, a three-dimensional image Pij resulting from the combination of the parallax images is created by a sum of products of these eight composite matrixes Mk(i, j) and sub-pixels Pk(i, j) of images corresponding to eight parallaxes. Note that (i, j) represents a laterally i-th and vertically j-th place in the composite matrix and the like.
                              P          ij                =                              ∑                          k              =              1                        8                    ⁢                                          ⁢                                                    P                k                            ⁡                              (                                  i                  ,                  j                                )                                      ·                                          M                k                            ⁡                              (                                  i                  ,                  j                                )                                                                        [                  Mathematical          ⁢                                          ⁢          Expression          ⁢                                          ⁢          1                ]            
Actually, however, the three-dimensional image is created by a bit-AND operation and addition or by a bit-OR operation instead of the mathematical expression 1. Here, assuming that the RGB sub-pixels being three sub-pixels on the flat display 132 each have a square shape, the plural apertures 134 of the parallax barrier filter 130 are arranged along a 71.6 degree angle in a diagonally right downward direction.
Further, in this case, the totally 24 sub-pixels of eight lateral sub-pixels×three vertical pixels form one unit, with red color, green color, and blue color being R, G, and B of each of the eight parallax images being arranged therein in a dispersed manner. That is, in any place of the parallax barrier filter 130 shown in FIG. 15, the apertures 134 corresponding to one picture element corresponding to the three pixels SP1, SP2, SP3 in red, green, and blue colors respectively are present in the 24 sub-pixels of the 2.67 lateral pixels (corresponding to eight sub-pixels)×three vertical sub-pixels. Consequently, the 24 sub-pixels form one unit of a three-dimensional image and this one unit is resolution of this three-dimensional image.
As a result, in the conventional parallax barrier filter of the eight-parallax type, though a high stereoscopic effect is obtained owing to reduced reverse view, not only resolution is reduced to one eighth but also brightness is reduced to one eighth of brightness obtained when the parallax barrier filter is not present, resulting in a dark image. This also applies to a conventional five-parallax type, and brightness is reduced to one fifth, resulting in a dark image.